Introduction
Branched-chain amino acids (BCAA) include leucine, isoleucine, and valine, among these supplements, which are essential amino acids and the body cannot produce them. BCAA acts as a nitrogen transporter and helps muscles to cooperate in the protein production process [2, 3]. Consumption of BCAA improves blood mononuclear cell proliferation and plasma glutamine concentration after long-term exercise [4].
Creatine kinase (CK) is a key enzyme that plays a role in muscle cell metabolism and accelerates the process of converting creatine to phosphate or vice versa [5]. Lactate dehydrogenase (LDH) is an enzyme that is found in the cytoplasm of all body tissues with different concentrations and increases the speed of the reaction in the conversion of pyruvic acid to lactic acid or vice versa in the anaerobic glycolysis pathway [5]. Most studies believe that BCAA is transformed into alpha-actoacids and then into succinyl-coa and acetyl-coa through a catabolic process and enters the Krebs cycle and ultimately helps energy metabolism during sports activities [8]. Exhaustive aerobic exercise causes muscle cell damage and release of muscle damage indicators (CK and LDH) into enters the bloodstream [8]. Vitamin E strengthens antioxidant enzymes and the body's immune system by reducing the resistance of tissues against lipid peroxidation caused by activity [12, 13]. Considering the effective roles of vitamin E supplement and BCAA consumption in muscle injuries, the question comes to mind if the simultaneous use of these two supplements has a difference effect on the indicators of muscle damage caused by exercise compared to their separate use? Therefore, this study aims to assess the effect of consuming BCAA after a period of vitamin E supplementation on muscle damage indicators in active women.
Methods
In this quasi-experimental study, 32 active female students (with regular activity at least two days a week) of Razi University in Kermanshah, Iran aged 18-23 years were selected using a convenience sampling method. After matching for body mass index, they were randomly divided into four groups including placebo (n=8), Vitamin E (n=8), BCAA (n=8), and Vitamin E+BCAA (n=). No metabolic diseases, BMI of 19-25, normal state based on PAR-Q score, no skeletal-muscular injuries, and no use of supplements or certain drugs were the inclusion criteria. The exclusion criteria were using vitamin E tablets regularly, having problems in performing the exercises, withdrawal or lack of cooperation.
Results
The findings showed that the exhaustive aerobic exercise increased the subjects' CK and LDH levels (P=0.001); their levels in the placebo (P=0.001) and Vitamin E groups (P=0.001 for LDH and 0.033 P for CK) was still greater than pre-activity values up to 48 hours after exercise. The LDH serum level was lower 48 hours after the activity compared to the values immediately after the activity in the BCAA and Vitamin E + BCAA groups (P=0.001). Furthermore, 48 hours after the activity, the LDH level of subjects in the BCAA group was lower than in the placebo (P=0.041) and Vitamin E (P = 0.021) groups, and the LDH of the subjects in the Vitamin E + BCAA group was also lower than in the placebo and Vitamin E group (P=0.001). The lowest amount of LDH was observed in the Vitamin E + BCAA group. The serum level of CK, 48 hours after the activity compared to its values immediately after the activity, significantly decreased in the BCAA and Vitamin E + BCAA groups (P=0.001) which was lower than in the placebo and Vitamin E groups (P=0.001). The lowest amount of CK was observed in the Vitamin E+BCAA group.
Discussion
According to the findings of the present study, the exhaustive aerobic exercise increased the levels of CK and LDH, which continued up to 48 hours after the activity. One month of Vitamin E consumption alone had no significant effect on the levels of CK and LDH enzymes. However, taking a dose of BCAA before exercise caused a significant decrease in the levels of the aforementioned enzymes 48 hours after exercise, and interestingly, the reducing effect of BCAA was greater when it was combined with vitamin E supplementation. Although the consumption of Vitamin E alone could not lead to a significant change (decrease) in the levels of CK and LDH enzymes, it had a reducing effect on the levels of the two mentioned enzymes. Since exercise affects the metabolism of amino acids, during the training conditions, there is an increase in the catabolism of amino acids. The oxidation of branched amino acids, especially leucine, with the increase of training intensity has been reported [30]. However, in this case, we can mention the anti-catabolic effects of consuming BCAA during and after exercise. Performing exercises regularly and with the proper intensity can cause many physiological adaptations in the body; however, in case of lack of physical preparation or in exhaustive activities, there is a possibility of injury in muscle cells [31].
Taking a dose of BCAA alone reduces the indicators of muscle damage for up to 48 hours after exhaustive aerobic activity; however, its effect seems to be greater when is combined with Vitamin E supplementation. It seems that leucine and isoleucine amino acids (not valine acid) are effective in reducing the indicators of muscle damage.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Guilan University of Medical Sciences (Code: IR.GUMS.REC.1398.137).

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
All authors equally contributed to preparing this article.

Conflicts of interest
The authors declared no conflict of interest.


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